The present invention relates in general to multilayer ceramic packages and, more particularly, to a probe for testing signals on transmission lines in multilayer ceramic packages.
The use of transmission lines to propagate electrical signals through multilayer ceramic packages is well known in the art. For example, it is common to build multiple layers of such devices by screen printing a conductive paste (e.g., silver, gold, copper, nickel, palladium, platinum or the like) on layers of a ceramic green tape according to a predetermined pattern. The layers are co-fired to form a dense ceramic package. Vias are typically formed for bridging electrical signals between conductive layers.
A typical transmission line comprises inherent distributed inductances 12 and 14 and shunt capacitances 16, 18, and 20 as illustrated in FIG. 1 which must be taken into consideration when designing the multilayer ceramic package.
In many applications, such as for radio frequency devices, the transmission lines couple components such as filters and baluns within the ceramic package. During the manufacture of these ceramic packages, or even after the package is manufactures, it is desirable to check the signal being propagated on various transmission lines coupling these components. However, the act of integrating a probe feed into the package (applying a conductor to the transmission line) changes the capacitance of the transmission line and adversely affects the signal being transmitted. FIG. 2 illustrates yet another transmission line comprising inherent distributed inductances 12 and 14, shunt capacitances 16, 18, and 20, and an additional capacitance 24 at node 22 from a probe. This additional capacitance 24 is undesirable as it introduces a discontinuity onto the transmission line resulting in a degradation of the transmitted signal.